1. Field of Invention
The present invention relates to an electrical system, and more particularly to a frequency detector in a clock data recovery system and a method for detecting frequencies.
2. Description of Related Arts
Frequency detectors are usually for comparing random data frequencies and clock frequencies in some serial communication systems. There are many traditional methods for detecting frequencies, such as comparing by counting and mutual sampling of orthogonal signals.
The method of comparing by counting for detecting frequencies usually takes a long counting period and answers slowly. Besides, it is difficult to accomplish detecting frequencies of the data and the clocks because a quantity of transition edges of the data is different from a quantity of clock. The method of mutual sampling of orthogonal signals for detecting frequencies has relatively bigger errors resulting from fluctuations introduced by the data, and still answers slowly.